1. Field of the Invention
The present invention relates to a drive mechanism for driving a movable mirror provided in a camera, and in particular to a shock-absorbing mechanism, provided in association with the drive mechanism, for the movable mirror.
2. Description of the Related Art
In SLR cameras, a movable mirror (quick-return mirror) is installed to be capable of moving up and down, more specifically, capable of rotating between a viewfinder light-guiding position (mirror-down position), in which the movable mirror is positioned onto a photographing optical path to reflect incident light from an object (object-emanated light) toward a viewfinder optical system, and a retracted position (mirror-up position), in which the movable mirror is retracted from the photographing optical path to allow the object-emanated light to travel toward the shutter. Rotation (swinging) of the movable mirror is limited by engagement of the movable mirror with a positioning member(s) provided in a mirror box which accommodates the movable mirror; however, if the rotating speed of the movable mirror is fast, the movable mirror bounces (vibrates) due to shock caused upon coming into contact with the positioning member (s). This bouncing of the movable mirror makes the image that is viewed through the viewfinder unstable, causing an adverse effect on the viewing performance of the viewfinder. Additionally, in a camera which is structured to lead light from an object to a distance measuring sensor and a photometering sensor via a movable mirror, a precise distance measuring operation or photometering operation cannot be performed during such bouncing of the movable mirror, which restricts sequential photographing performance. Because of such reasons, various shock-absorbing mechanisms which absorb shock of the movable mirror when it rotates to reduce bouncing of the movable mirror have been proposed. Examples of conventional shock-absorbing mechanisms include a type of shock-absorbing mechanism which makes the movable mirror come into contact with an elastic member and another type of shock-absorbing mechanism which makes the movable mirror come into contact with a movable member which is biased tending to move by a biasing member.
A high positioning accuracy of the movable mirror is required specifically when the movable mirror is in the aforementioned viewfinder light-guiding position, in which the movable mirror exerts a direct influence on the viewing performance of the viewfinder, and when the movable mirror is in the aforementioned retracted position, in which an exposure operation is performed; accordingly, it is necessary for the positioning of the movable mirror to be made using a special positioning member and for the shock-absorbing mechanism to be constructed so as not to interfere with the positioning that is made using this special positioning member. In other words, a shock-absorbing mechanism for a movable mirror provided in a camera is required not only to reduce bouncing of the movable mirror when rotating, but also is required not to interfere with the positioning of the movable mirror upon reaching either rotational limit thereof; however, satisfying these requirements tends to complicate the structure of the shock-absorbing mechanism.
Furthermore, if the biasing force that acts on a shock-absorbing movable member (s) (shock-absorbing member) is strengthened, the absorbing efficiency of the moving energy of the movable mirror increases; however, if the biasing force becomes too strong, the load on the movable mirror becomes excessive, so that there is a risk of not being able to reliably move the shock-absorbing movable member to a position corresponding to a mirror-up position or a mirror-down position of the movable mirror. On the other hand, if the biasing force that acts on the shock-absorbing movable member is too weak, a sufficient shock-absorbing capability cannot be obtained. Hence, there is a need for a shock-absorbing mechanism which can reliably operate a movable mirror while having a high shock-absorbing capability. In an attempt to solve the above-described problem, it is conceivable to provide an independent drive mechanism that moves the shock-absorbing movable member to a predetermined position at the final stage of the mirror-up operation/mirror-down operation; however, the number of components increases and the structure therefor becomes complicated, having the disadvantage of increasing (manufacturing) costs and increasing the size of the camera itself.